1. Field of the Invention
The present invention relates to a tuning fork type piezoelectric resonator made of, for instance, quartz crystal or the like, a method of manufacturing the same and an electronic part using the same.
2. Description of the Related Art
The tuning fork type quartz resonator has long been adopted as a signal source for pacing a wrist watch owing to its being compact, inexpensive and having a low power consumption, and the uses thereof are still expanding. The CI (crystal impedance) value of this quartz resonator is required to be as low as possible to reduce power loss, and a quartz resonator with a groove formed therein to enhance vibration efficiency is being used for this purpose.
The tuning fork type quartz resonator is provided with a pair of vibrating arms 2a and 2b on a base 1 as shown in FIG. 9, and grooves 31 and 32 are respectively provided on both main surfaces of the respective vibrating arms 2a and 2b. Excitation electrodes (not shown) for exciting fork vibration based on bending vibration are formed on these grooves 31, 32 and the respective vibrating arms 2a, 2b. Metal films 50a and 50b for adjusting frequency by adjusting the weight of the vibrating arms are formed on both front and back surfaces at the tips of the vibrating arms 2a and 2b. 
The metal films 50a and 50b for adjusting frequency include a chromium (Cr) film 10, a gold (Au) film 11, and a chromium (Cr) film 13, which are stacked on the surface of the vibrating arms 2a and 2b in this order as shown in FIG. 10, and further include a gold (Au) film 12 serving as an adjusting weight being stacked further thereon. Incidentally, FIG. 10 is a schematic sectional view of a sectional part along the A-A line in FIG. 9. The metal films 50a and 50b for adjusting frequency thus structured are used to adjust the vibration frequency of the tuning fork type quartz resonator to, for instance, 32.768 kHz. Specific description of making adjustment to the vibration frequency is as follows. First, an oscillation circuit is connected to one quartz resonator among plural pieces of quartz resonators which are formed on a sheet of quartz wafer to measure the frequency before adjustment. Then, the metal films 50a and 50b for adjusting frequency are irradiated with a laser beam so that the gold (Au) film of the adjusting weight is sputtered to conduct rough adjustment to adjust the frequency close to 32 kHz. At this time, irradiation pulse number of the laser is counted. Thereafter, ionized argon particles obtained by discharging argon (Ar) are allowed to hit at the metal films 50a and 50b for adjusting frequency so that the gold (Au) film is sputtered to complete fine adjustment to the target frequency. The fine adjustment is conducted by sputtering the gold (Au) film with argon ions while monitoring the vibration frequency of the quartz resonator so as to adjust the thickness of the gold (Au) film. At this time, the irradiation amount of the argon (Ar) plasma is counted.
Next, based on the irradiation pulse number of the laser and the irradiation amount of the argon (Ar) plasma obtained from the above-described quartz resonator, the metal films 50a and 50b for adjusting frequency are shaved by a laser and argon (Ar) plasma for plural quartz resonators formed on a sheet of quartz wafer so as to match with the vibration frequency.
However, the above-described adjustment of the vibration frequency has the following problems. In a rough adjustment of the frequency of each quartz resonator, accurate positioning between the laser and the quartz wafer stage and degrees of melting of the metal films 50a and 50b for adjusting frequency with a laser are varied. Accordingly, time required for the rough adjustment is varied, which creates variation of time duration for the fine adjustment. When time for the fine adjustment is prolonged, time for irradiation with the argon (Ar) plasma also increases. As a result, the heating value of the quartz resonator increases. Since the vibration frequency of the tuning fork type quartz resonator is apt to be affected by heat, in other words, sensitive to heat, it is difficult to realize adjustment accuracy of high vibration frequency if the heating value varies in this manner.
Whereas the Patent Document 1 describes that the electrodes for finely adjusting frequency are formed in stripes on both front and back surfaces of a tuning fork arm, and, a beam of laser is allowed to irradiate the electrodes for finely adjusting frequency on the front surface of the tuning fork arm so as to perform fine adjustment of frequency. However, it is impossible to adjust the vibration frequency with high accuracy using this technology.
[Patent Document 1] Japanese Patent Application Laid-open 2003-133885 (paragraph 0040, FIG. 1)